The on-going miniaturization of semiconductor technology has enabled a remarkable diversification of functionality embedded in semiconductor devices such as integrated circuits (ICs), which in some cases has led to the provision of near-holistic solutions on a single device. For instance, semiconductor device miniaturization has led to the integration of one or more sensors into a single semiconductor device, and the deployment of such devices can be seen in widely different technical areas, e.g. automotive applications, healthcare applications, industrial gas flue monitoring and so on.
For instance, over the last few decades, sensing transistors have been added to ICs, e.g. chemical field effect transistors such as ion-sensitive field effect transistors (ISFETs), enzyme-functionalized field effect transistors sensitive to biomolecules (ENFETs) and so on. These field effect devices work on the principle that the channel region of the devices is exposed to the medium to be sensed, such that the current flowing through the channel region becomes a function of the analyte of interest. To this end, the device may comprise a functionalization layer separated from the channel region by a gate oxide or a functionalized extended gate acting as a floating gate, with the gate potential being defined by the level of interaction between the analyte of interest and the functionalization layer.
One of the major challenges in providing sensing functionality on an electronic device such as an IC is to ensure that the semiconductor device can be produced in an economically feasible manner. This is for instance a particular challenge when sensing elements of sub-micron dimensions, e.g. nano-elements such as nanowire-based transistors, are to be integrated in the semiconductor device, as it is not at all straightforward to manufacture such nano-elements using processing steps that are compatible with the manufacturing process of the overall semiconductor device. Hence, the integration of such dedicated elements can lead to a significant increase in the complexity of the manufacturing process of the semiconductor device, thereby significantly increasing the cost of such devices.
A particular problem in this respect is that when the sensing medium is a fluid, e.g. a liquid or gas, the sensor arrangement usually requires the presence of an external reference sensor or electrode to compensate for sensor drift, i.e. the time-varying response of a sensor to an analyte of interest. An example of such an arrangement is disclosed in US 2004/0136866 A1, in which a reference electrode is placed into contact with a fluid to be analysed in order to control the potential of the solution relative to the semiconductor nanowire sensing element. However, the inclusion of a reference sensor or electrode can further complicate the design of the sensor arrangement, which therefore can further increase the cost of the electronic device. Moreover, the surface of the reference electrode can be prone to fouling, in which case the sensor readings can become unreliable.